Variable volume pumping mechanism



y 1959 c. E. ADAMS ET AL 2,887,060

VARIABLE VOLUME PUMPING MECHANISM Filed June 22, 1953 '7 Sheets-Sheet 1 IN V EN TORS CECIL EJDAMS BY WILLIAM EESCNLIIMN y 19, 1959 c. E. ADAMS ET AL 2,887,060

VARIABLE VOLUME PUMPING MECHANISM Filed Jl me 22, 1953 7 Sheets-Sheet 2 INVENTORS CEUL E. ADAMS BY WILLIAM EAESOMMAN I May 19,1959

Filed June 22, 1953 C. E. ADAMS ET AL VARIABLE VOLUME PUMPING MECHANISM 7 Sheets-Sheet 3 CECIL E. ADAMS y WILLIAM E. ESCHLIMAN May 19,1959 c. E. ADAMS ETAL VARIABLE VOLUME PUMPING MECHANISM 7 Sheets-Sheet 4 Filed June 22, 1953 IN V EN TORS (IL 5- ADAM BY WLLIAM E. ESCHHMAN May 19, 1959 c. E. ADAMS ET AL 2,387,060

VARIABLE VOLUME PUMPING MECHANISM Filed June 22, 1953 7 Sheets-Sheet 5 IB'S INVENTORS CECIL E. ADAMS y WILLIAM EESCNUMAN y 1959 c. E. ADAMS ET AL 2,887,060

VARIABLE VOLUME PUMPING MECHANISM Filed June 22, 1953 7 Sheets-Sheet 6 INVENTORS CECIL E. ADAMS WILLIAM E. ESULMAN May I9 1959 c. E. ADAMS ET AL I 2,887,060

h VARIABLE VOLUME PUMPING MECHANISM I Filed June 22, 1955 7 Sheets-Sheet 7 INVENTORS CECIL I. ADAMS By WILLIAM LISCHLIMAN United States Patent ()flice 2,887,060 Patented May 19, 1 959 2,887,060 VARIABLE voLUMn PUMPING MECHANISM Application June 22, 1953, Serial No. 363,098

13 Claims. (Cl. 103-42) This invention relates generally to hydraulic apparatus and is more particularly directed to an improvement in fluid pumping and pressure producing mechanism. Still I more particularly the invention is directed to a power driven pump and valve combination designed for operation at variable speeds and having all the advantages of a.v hydraulically balanced, constantvolume pump construction yet secure a supply of fluid the volume of which may be varied. at will.

An object of this invention is to provide a fluid pumping mechanism which will circulate a large volume of cool fluid under low pressure from a reservoir through the pump and back to the reservoir during, the time the mechanism is maintaining. a predetermined pressure in a hydraulic system but delivering little or no fluid thereto, the mechanism thereby being held at a safe operating temperature.

A further object of this invention is to provide a fluid pumping mechanism having a delivery volume which is directly proportional to the torque of a torque motor, the mechanism being particularly suitable for use as a servo device, operating. either in one direction or across a center position irrespective of working pressure or pressure variations.

A still further object of the invention is to provide a fluid pumpingmechanism having avolume control means which will be relatively free from forces imparted by the fluid tending to. change the setting thereof so that the control may be accurately adjusted by a relatively weak, short stroke, torque motor to secure an eflective volumetric output from the pump which will be directly proportional to the strength of current applied to the torque motor.

An object of this invention is to provide a fluid pumping mechanism having a pump of the type shown inour copending application Serial No. 352,102, filed April 30,, 1953, now Patent No. 2,832,199, and a valve means by which the output of one or more of the pumpingse'ctions of the pump may be recirculated through the pump or by-passed back to the system reservoir under no pressure so that the eifective output of the pump' may be varied with a consequent variation in the operating horsepower requirements.

Also, an object of this invention is to provide a fluid pressure generating system having apump with a plurality of independent discharges of diflerent volumes and control valve mechanisms operative to" combine all or 2, the volume of fluid made available for use will be varied and the horsepower requirement for operating the pump correspondingly varied. 1

A further object of the invention is to provide a hydraulic pressure source having a vane pump and valve combination for supplying any desired volume of fluid from zero to a predetermined maximum, the pump having a plurality of separate outlets, the valve being respom sive to pressure to move to diiferent positions in which various combinations of the output of the separate outlets may be' secured, the valve also serving to vary the output of each combination so that the supply may be infinitely varied between substantially zero volume and the designed maximum capacity, the horsepower requirement for operating the pump varying in a somewhat sim-- ilar manner.

A still further object of the invention is to provide a hydraulic pressure source of the type mentioned in the preceding paragraphs with a reversing valve through the operation of which a fluid motor may be caused to oper ate at any speed in a forward or reverse direction by merely moving the control elements .of the reversing, valve in either of the two directions, thus, the same .results may be secured as are given by a cross center pump of the piston type.

Another object is to provide a hydraulic pressure source of the type mentioned in several ofthe preceding paragraphs and in which some of the pump volume is by-passed to the reservoir, resistance being applied to the flow being by-passed to cause apredeterminedpressure which is employed to operate ajet type ofbooster to charge the inlet of the pump to avoid cavitation at high speeds of operation.

A more specificobject of the invention is to provide a hydraulic pressure source having a vane type pump with a plurality of pumping sections of difierent capacities and independent outlets and a valve mechanism with a plurality of inlet ports communicating with the outlets of the pump, such outlets being connected with a line containing a variable orifice for creating a pressure differential which is employed to cause a spool in the valve mechanism tomove to connectone or more of the valve inlet ports with exhaust to by-pass a variable part of the volume of fluid delivered by the pump to maintaina selected volume available for use, the adjustment of the orifice serving'to select the volume of'fluid available for by-pass any one or more of the independent discharges r to" the end that the volume of fluid available for use may be selectively varied from a maximum potential volume requiring a certain horsepower to operatethepumpto'a minimum volume requiring less horsepower for pumpopjoration.

An object of the invention is to provide a pressure source having a pump with a plurality of pumping sections with independent outlets, and avalve mechanism selectively operable to by-passfluid issuing from different combinations. of the independentflpump outlets wherebyof fluid delivered by the pump to apparatus for using Another object of the invention is to' provide a hydraulic pressure source having a pump which has a plurality of independent outlets of different volumes and a valve mechanism operative to by-pass some or all of the volume issuing from one or more of the pump outlets, the valve mechanism having a number of inlet ports corresponding to the outlets'of the pump and connected therewith and a spool valve with a plurality of openings serving to connect, one or a combination of the inlet ports with exhaust to effect the by-passing of fluid from one 31 more of the outlets of the pump, an orifice being. arranged in a line conducting fluid from said pump to create a pressure drop, the contrasting pressures of which are utilized to move the spool valve, resilient means tending to return the spool valve to a position in whichno fluid Will be by-passed.

' An object also is to substitute a relief valve for the orifice in the combination set forth in thepreceding para graph, the relief valve serving to direct the total-volume the same until a predetermined pressure is built up and then apply some of thepressure to the spool valve toef fect itsmovement to a position to bypass all the fluid in excess of that required tomaintain the predetermined pressure and proportionately reduce the horsepower consumption of the pump.

Further objects and advantages of the present invention will be apparent from the following description, reference being had to the accompanying drawings wherein a preferred form of embodiment of the invention is clearly shown.

' In the drawings:

Fig. 1 is a diagrammatic view of a hydraulic pressure source formed in accordance with the present invention, part of the mechanism used therein being shown in section;

Fig. l-A is a fragmentary diagrammatic view of a slightly modified pressure source;

Fig. 2 is a similar view of a modified hydraulic pressure source formed in accordance wtih the invention, parts of the-mechanism employed being shown in section;

Fig. 2-A is a fragmentary diagrammatic view illustrating a modification which may be employed in the systems;

Fig. 3 is also a diagrammatic view of a further modified form of pressure source in a hydraulic system;

Fig. 4 is a diagrammatic view of a still further modified I a passage 33. Thus far described, the pump 20 is substantially identical with at least one form of pump shown in the above-mentioned copending application. It should be obvious that as the rotor 23 revolves, the fluid transfer pockets 25 will fill with fluid as they pass the inlet ports 26 and will discharge fluid through the outlet ports 27 and 28 as they pass such ports, part of the contents of each pocket being discharged through ports 27 and the remainder, except for the clearance volume, through ports 28.

Passages and 31 are connected with another passage 34 which conducts the fluid from the pump to a point of use. Check valves of any suitable design are arranged between the line 34 and lines 30 and 31 to prevent fluid from flowing from line 34 back to ports 27 or 28. It is a known fact that when a pump with a certain potential volume while operating at one speed is driven at a different speed, the volume changes and the operating power requirements change likewise. An object of this invention, therefore, is to provide mechanism whereby a predetermined volume of fluid will be delivered at all times through the line 34 irrespective of the rate of operation of the pump, within reasonable limits, and without the usual increase in operating power requirements when the rate of pump operation is increased above that required to produce the predetermined volume of 'fiuid. To secure this object, mechanism in the form mechanism being shown in condition to direct the entire volume to the point of use;

Fig. 6 is a diagrammatic view of the valve portion of the system shown in Fig. 5, the valve mechanism being shown in-condition to by-pass a portion of the volume from one set of pump output ports; and

Figs. 7, 8 and 9 are similar views showing the parts of the valve mechanism in different positions of operation to either bypass all of the volume from one set of pump output ports, part of the volume from another set of pump output ports, or all of the volume from the latter set of pump output ports plus part of the fluid from the first set of pump output ports.

Referring more particularly to the drawings, various modifications of the invention have been shown. These all employ the same fundamental principles adapted to slightly different purposes. A simple form of apparatus for carrying out the invention has been shown in Fig. 1 wherein .a pump 20 of the type illustrated in the copending application has been diagrammatically shown. The pump 20 is of the vane type and has a plurality of pumping sections which may be of equal capacity but are preferably of diflerent capacities. The pump illustrated is of the balanced type, that is, it has radially oppositely disposed sets of pumping sections so that radially opposite parts of the pump will be exposed to equal pressures. In pump 20, a cam ring 21 controls the radial movement of vanes 22 which are disposed for sliding movement in and rotary movement with a rotor body 23. As usual in vane pumps, the vanes 22 engage a peripheral wall 24 and end walls, located one at each side of the rotor 23, and cooperate with the rotor 23 to form fluid transfer pockets 25. Due to the shape of the peripheral wall 24 the pockets 25 vary in volumetric capacity as the rotor 23 revolves, the capacity increasing while the pockets 25 communicate with inlet ports 26 and decreasing while the pockets 25 communicate with outlet ports 27 and 28. The peripheral wall 24 in the pump 20 is so formed that a certain percentage of the volume of each pocket 25 will be expelled through outlet ports 27 while the pockets 25 communicate therewith and either the same, or, depending upon the use to which the pumpis to be placed, a difierent percentage will be expelled through outlet ports 28 while the pockets 25 communicate with such ports during the rotation of the rotor. Ports 27 com municate with one another through a passage 30 while ports 28 are connected by passage 31. The inlet ports 26 are connected with one another and a reservoir 32 by ofa valve 36 is provided to by-pass or recirculate variable portions of the fluid transferred from the inlet ports in the'line 34. The size of the orifice 37 selected will be determined by the volume required to perform the desired operations. The pressure dilferential is employed to operate the valve 36 in a manner to be described.

The valve mechanism 36 includes a casing 38 which forms a chamber 40. Casing 38 may be made separate from the housing of the pump 20, but it is preferably made integral therewith. Chamber 40 is provided with a plurality of inlet ports 41 and 42 (corresponding in number to the number of outlets or sets of outlets 27 and .28 of the pump 20) and an outlet or exhaust port 43. Ports 41 and 42 are directly connected by lines 44 and 45 respectively, with passages 30 and 31 and consequently with ports 27 and 28. Chamber 40 is formed for the slidable reception of a valve spool 46 employed to control communication between inlet ports 41 and 42 and outlet port 43, this latter port being connected with reservoir 32 by a line 47. If it should be desired to recirculate some or all of the fluid flowing from outlet port 43, the line 47 could be connected with passage 33, however, by directing the exhaust from valve 36 to the reservoir 32 the fluid may be cooled. A spring 48 is disposed between one end of the chamber 40 and the adjacent end of the spool 46, the spring tending to maintain the spool in a position at one end of the chamber 40. In thisposition, the spool prevents communication between either of the inlet ports 41 and 42 and the outlet port 43, and the entire output of pump 20 is directed through check valves 35 to line 34.

The apparatus or fluid pressure source shown in Fig. 1 should be so designed that when the pump 20 is operating at a predetermined minimum rate, the required volume, at the pressure necessary for the desired operations, will be delivered through line 34. This line may be provided with a suitable relief valve 50 to limit the pressure generated in the system. If the rate of operation of the pump should be increased beyond that pre-,

determined minimum, fluid in excess of that necessary for the desired operation will be pumped. In a conventional hydraulic system, this excess fluid would spill over the relief valve 50 with a consequent increase in the heat of the fluid and loss of efliciency in the system. To avoid this loss the valve 36 and associated orifice 37 have been provided. i

The spool 46 of the valve 36 is formed with a plurality of sets of ports 51, 52 and 53, the latter being disposed to establish constant communication between the interior of the spool 46 and outlet port 43. When the pump output increases, the pressure at theinlet side of orifice 37 starts to increase and the balance of forces on the ends of spool 46 to which the pressures on the inlet and outlet sides of the orifice 37 are applied through lines 54 and 55, respectively, will be upset. Since the greater pressure is applied to the end of the spool 46 opposite the spring engaged end, the spool 46 will start to move in response to this pressure. Initial movement of the spool 46 will cause ports 51 to start to establish communication between port 42 and the reservoir 32 through the interior of the spool, port 43 and line 47. Some of the fluid from ports 28 of the pump 20 will'thus be by'-passed to the reservoir 32. Continued increase in the pump output will cause continued movement of the spool 46 until the entire volume flowing from ports 28 will be by-passed; When this condition occurs the portion of the pump Withthe outlet ports 28 will be" unloaded or operating under no pressure and the operating power requirement proportionately reduced! If the pump output should continue to increase the spool 46 wili move further in opposition to spring 48 and ports 52 will start to establish communication between inlet 41 and the reservoir 32. The occurrence of this condition causes the by-passing' of part of the fluid discharged from ports 27 of the pump to reservoir 32. The quantity of fluid by-passed will, as before, he that fluid in excess of the volume required to maintain the pressure differential caused by the orifice 37. As long as theoutput of pump 20 exceeds such volume, spool 46- will remain in position to by-pass the excess to the reservoir 32. If the entire output of the pump section exhausted through the ports 28 isby-passed, and no pressure exists inthis section, the horsepower requirement for operating this section of the pump will be reduced to a minimum. When the pump output decreases spring 48 will move spool 46 back toward the position in which. no fluid is by-passed. In this form of the invention the change in volume of fluid bypassed will take place smoothly while the change in operating power requirements will be by predetermined percentages of the total requirements. This should be obvious since operating power requirements for any pump section will continue unabated until the section is completely by passed to tank underno pressure at which time the operating horsepower requirement will be reduced.

Asan example, assume that the peripheral wall 24 of the pump 20 is so formed that twice as much fluid is discharged through ports 28 as is discharged through ports 27; Then when spool 46 is moved to such position that. all of the fluid from ports 28 is by-passed, the horsepower requirement for operation will be only one third of that required if no fluid were by-passed, because two thirds of the potential volume of the pump is being by-passed under no pressure. It should beevident that the power re-- quired for pump operation when certain ports arevented. could be further reduced by designing the pump so that the volume of liquid discharged through the ports which are fully connected with the reservoir would be increased and the volume discharged through the other ports underpressurewould be decreased; In the description thus far given the orifice 37 has beenof afixed size which will permit the passage of a certain volume of fluid ata predetermined pressure diflerential. As shown in Fig. 1A. line 34 could he provided with a variable orifice 37-A. through the adjustment of which other volumes at such predetermined pressure dificrential would be permitted to flow. In all instancesthe orifice 37-A will be adjustedto secure a desired volume, then the system will operateas previouslydescribed. From the foregoing itwill-be seen.

that valve functions in a dual capacity. It seiects the pump outletor outlets from which the fluid will be supplied to the point of use and then regulates the volume of fluid directed from the outlets selected, to the point of use. In most installations of the apparatus or fluid pressure source shown in Fig. 1, the orifice 37 will be se-' lected to give certain results. If other results are desired a difierent size orifice will be selected. In some installations, depending upon the use to which the system is'to be placed, the variable orifice 37-A may be employed. This orifice may be adjusted to adapt the system to different conditions but during operation under any set of conditions the orifice will remain at the selected setting. The system illustrated is particularly adaptable for use where the pump is to be operated by a prime mover, such as an internal combustion engine, not shown, the operating speed of which may vary widely. When the speed of the prime mover increases there will be a tendency for the pressure differential to change due to the additional volume being delivered by the pump. This tendency of the pressure difierential to change causes the valve 36 to operate to by-pass the increased fluid and the system operates the same as it did before the change in speed of the prime mover.

In Fig. 2 both the pump and the valve have been modified tosecure a greater variety of conditions of operation. Like the pump 20, the pump 56 includes a cam ring 57 forming a peripheral Wall 58 for a rotor chamber 60. A rotor 61 is supported for rotation in the chamber, this rotor being similar to the rotor in the pump 20, but having a greater number of vane slots and vanes 62 which are thinner than the vanes 22. The increase in number of vanes is desirable because the pump 56 has one more set of pumping sections and output ports than the pump 20. In the pump 56, the vanes are not spring pressed toward the chamber wall 58 but are urged in this direction at all times by fluid pressure introduced into the inner ends of the vane slots in a manner to be described.

Pump 56 is also of the balanced type having diametrically positioned inlet and output ports arranged in sets. The inlet ports 63 are connected with one another and the reservoir 64 by passage 65, ports 63 being in reg-' istration with the portionsof the peripheralwall 58- which cause the fluid transfer pockets between the vanes to increase in volumetric capacity. Three'sets ofoutlet or output ports 66, 67 and 68 are provided, the portions ofthe peripheral wall 58 registering with these ports being shaped to cause the pockets 25 between the vanes to decrease" in volumetric capacity. The ratio of decreasebe tween the pockets registering with or communicating with the various ports 66, 67 and 68 may vary according to the desires of the manufacturer or the uses to which the mechanism is placed but one desirable ratio is 4 parts to 2 parts to 1 part for ports 66, 67 and 68, respectively. In other words, as the pockets 25 between the vanes 62 communicate with port 66 during the rotation of the rotor 61 four sevenths of the volume of fluid in each pocket will be discharged through port 66. When each pocket communicates with port 67 two sevenths of the volume of fluid will be discharged and the remaining one seventh will be discharged while the pocket communicateswith port 68. Ports 66 are connected by passage 70, ports 67 are connected by passage 71 and ports 68 are connected by passage 72. These passages 70, 71, and 72 connect with a line 73 leading to the point of use. Check valves 74 are provided to prevent back flow from line 73 to passages 70, 71' and 72 as in the form of the invention first described. It will be obvious that the rotation of rotor 61 in the direction indicated by the arrow will cause fluid to be drawn from reservoir 64 and discharged by the pump through line 73. Fluid from this line is conducted through branch line 75 to a groove in the rotor and is admitted to the inner ends of the vane slotsto urge the vanes 62 in an outward direction.

To accomplish certain objects of the invention, a modifiedformof selector andregulator valve 76 has been provided. This valve issimilar to valve 36 both in construction and. function. Its operation is slightly different. Valve 76 has a casing 77 with inlet ports 78, 79 and 80 which are connected with passages 70, 71 and 72, respectively. Casing 77 forms a chamber 81 having an outlet port 82 connected by line 83 with reservoir 64. Chamber 81 is formed for the slidable reception of a hollow spool valve element 84 having a plurality of sets of ports 85,86, 87, 88, 89, 90, and 91 formed therein in particularly spaced relation. A stem 92 projects from the spool through one end of the casing and suitable means may be connected therewith to move the spool 84 selectively to any one of eight positions in which it will be yieldably retained by a spring pressed detent 93 engaging one of a plurality of grooves 94 formed in the stem.

When the detent 93 is disposed in the first groove, as shown, all of the output from all of the sections of the pump 56 will be directed through line 73. If, as in the previous description, the rate of operation of the pump is increased the volume of fluid delivered to line 73 will also increase in proportion. Should it be desired to maintain the volume and operating power requirement selected previously or reduce the volume and the horsepower requirement while maintaining the rate of pump operation, the valve spool 84 may be moved toward the left as viewed in Fig. 2. Movement of the valve spool 84 until the detent 93 engages in the second groove 94 will cause ports 85 to register with inlet 80 and connect pump outlets 68 directly with reservoir 64 via the inside of the spool 84, chamber 81, port 82 and line 83. All the output of the pump through ports 68 will then be by-passed under substantially no pressure to the reservoir 64. If, as previously assumed, one seventh of the pump output is discharged through ports 68, the volume of fluid flowing through-line 73 will be reduced by this amount as will also the operating horsepower requirement if the rate of pump operation is maintained. By moving the spool 84 far enough to cause the detent 93 to engage the third groove 94, ports 85 will be moved out of registration with port 80 and ports 89 in spool 84 will be disposed in registration with ports 79 and the pump outlets 67 will be directly connected with reservoir 64. The output from outlets 67 will, therefore, be by-pa ssed under substantially no pressure to the reservoir 64. Since, as assumed, two sevenths of the total output of the pump 56 issues from ports 67, the volume of fluid flowing through line 73 will be reduced by this amount and the operating power requirement will also be reduced proportionately.

The fourth position of the spool 84 as determined by the fourth groove 94 maintains the connection between pump ports 67 and reservoir 64 through ports 79 and 89 and re-establishes the connection between pump ports 68 and reservoir 64 through ports 80 and 86. In this position of the spool 84, the total volume of fluid issuing from ports 67 and 68 will be by-passed to reservoir 64 under no pressure. This volume will be three sevenths of..the pump output. As pointed out previously, since this portion of the pump is operating under no load the operating power requirement for the pump 56 Will be reduced proportionately. When the spool 84 is shifted until the detent 93 engages in the fifth groove 94, both ports 79 and 80 will be closed, and port 91 will register with port 78 establishing a direct connection between pump outlets 66 andthe reservoir 64. Since these outlets 66 have four sevenths of the pump output issuing therefrom, the discharge through line 73 will be reduced by that much. Once again it is emphasized that since four sevenths of the load on the pump is eliminated the operating power requirements of the pump 56 will be reduced by the same amount.

Movement of the spool 84 to engage the detent 93 in the sixth groove reestablishes the connection between pump outlets 68 and the reservoir 64 through ports and 87 and the output of the pump through outlets 68 is then combined with the output from outlets 66 and directed to reservoir 64 under no pressure. This com bined output will total five sevenths of the pump discharge and the volume flowing through line 73' will thus be reduced by this amount. The horsepower required to operate the pump 56 will be reduced in proportion.

The seventh position of the spool 84, determined by the location of the detent in the seventh groove, places port 87 beyond port 80 and the output from pump outlets 68 will again be directed to line 73. Ports will, however, be disposed in registration with ports 79 so that the. output from ports 67 will be combined with the output from ports 66 and directed to reservoir 64 under no pres sure. Since outlets 66 discharge four sevenths of the pump output and outlets 67 discharge two sevenths thereof, six sevenths of the total output of pump 56 will be lay-passed under no pressure to reservoir 64 in the seventh position of the valve spool 84 and the operating power requirement of pump 56 will be reduced by six sevenths.

In the eighth and last position of the spool 84 all of the output of the pump 56 will be directed to reservoir 64 and the pump will be completely unloaded.

In all of the foregoing examples of the various positions of operation of valve 76 it was assumed that the pump was being driven at a constant speed. If, however, the speed of the pump 56 is increased the volume of fluid delivered through line 73 and the operating horsepower requirement for pump 56 will increase unless spool 84 is adjusted to compensate for the increased output vol-, ume of pump 56.

Sometimes when a fluid pump is operated at high speeds, the fluid transfer pockets between the vanes 22 pass the inlet ports so rapidly that insufficient fluid is ad-. mitted to the pockets to fill them. The pockets may then be under a partial vacuum and/or contain foamy fluid. This condition is referred to in the trade as cavitation and is very undesirable. To eliminate or minimize it as much as possible, the system may be provided with a jet type of booster means 95 (Fig. 2-A). To eflect its operation the exhaust line 83 may be provided with a restriction 96 to impose a suitable pressure on the fluid being by-passed. Fluid at this pressure is directed from line 83 at a point in advance of the restriction, through a passage 97 to a jet nozzle 98 which is surrounded by a casing the inlet of which communicates with the reservoir 64. Fluid under pressure flowing from the jet 98 causes additional fluid to be drawn from the reservoir and directed under booster pressure through lines 65 to the inlet ports 63 of the pump. Due to this booster grlescslure the pockets will be more rapidly and completely The construction of the fluid pressure source according to the apparatus or invention minimizes the neces sity for a boosting mechanism, however, because the cavitation occurs only when the pump is operating at high speeds and full volume is not generally required. At this time the volumetric capacity of the fluid transfer pockets between the vanes 22 is partially reduced while they communicate with the first set of output ports 66 and any foamy oil will be by-passed through such ports. If only a vacuum has been caused it will be dissipated by the reduction in capacity of the pockets. When the pockets communicate with the next output ports 67 solid oil will be discharged to the system for use and the eif ects of cavitation avoided.

In Fig. 3 the fluid pressure source is modified to operate as a pressure compensator controlled pump. The

pump in this form of the invention is substantially identical with the one shown in Fig. 2. and the same reference enemas numerals, where applicable, have been employed. The fluid outlet line 73 is connected with the Work, repre sented in this instance by a fluid motor 103. Exhaust line 104 extends from the motor 103 to the reservoir 64 to complete the hydraulic system.

The pump 57 is combined with a valve mechanism 105 which is similar in certain respects to the valves 36 and 76 previously described. Valve mechanism 105 includes a casing 106 forming a spool chamber 107 with inlet ports 108, 109 and 110, an exhaust port 111 and a control port 112. The inlet ports 108, 109 and 110 correspond in number with the sets of pump output ports and each inlet port is connected with a different set of pump output ports. Port 108 is connected with output ports 66 by passage 113, port 109 is connected with output ports 67 by passage 114 and passage 115 connects port 110 with output ports 68. Exhaust port 111 is connected with the pump inlet lines 65 and the reservoir 64 by an exhaust passage 116. Control port 112 is connected with the pressure line 73 by passage 117 which contains a relief valve 118. The latter valve may be of any type, a spring loaded valve designed to operate at a predetermined pressure to permit fluid to flow from line 73 to passage 117 being suitable.

The chamber 107 receives, for sliding movement, a spool member 120 which is urged by a spring 121 toward the end of the chamber communicating with the control port 112. Spool 120 is formed with spaced sets of openings 122, 123 and 124, which are disposed to suecessively register with the inlet ports 108, 109 and 110 and connect the pump output ports communicating therewith with exhaust passage 116. Spool 120 is also provided with a bleed port 125 to permit fluid to escape from the end of chamber 107 and line 117 communicating therewith when valve 118 closes.

In the operation of the system shown in Fig. 3 pump 56 is driven in the direction indicated by the arrow and the entire output from all of the pumping sections will be directed through line 73 to the motor 103 until a predetermined pressure in line 73 is reached. At this time valve 118 will open to permit fluid to flow through line 117, port 112 and bleed port 125 to chamber 107. The pressure of this fluid will be applied to the end of spool 120 to move it in opposition to the force of spring 121. The initial movement of spool 120 will establish. communication between port 158 and exhaust port 111 and some of the output from pump ports 66 will be bypassed. After spool 120 has moved far enough to completely vent the pump ports 66 under substantially atmospheric pressure, the operating horsepower requirements of pump 56 will be reduced in proportion to the decrease in fluid directed to line 73 as in the other forms of the invention. Further movement of the spool 120 to connect pump ports 66, 67 and 68 to exhaust port 111 will effect a further corresponding decrease in operating horsepower requirements of pump 56. It will. be observed that by using the relief valve 118 to control the application of fluid under pressure to valve 105 all the fluid in excess of that required to maintain a predetermined pressure will be by-passed. If the, volume of fluid by-passed is suflicient, a savings in operating horsepower of pump 56 will result.

Fig, 4 also shows a hydraulic system having a source of fluid pressure embodying the present invention. Here again the pump in this system is substantially identical with the pump shown in Fig. 2 and similar numerals ofi reference are used. The system shown in Fig. 4 is a closed system, the line leading from reservoir 64 being provided with a check valve 126 to permit make up fluid to be drawn into the system but prevent loss of fluid therefrom.

The output ports of pump 56 are connected, as in the forms of the invention shown in Figs. 2 and 3, with a. line 73 leading to the mechanism to be operated or the work to beperformed. In Fig. 4 this mechanism is indi cated by the fluid motor 127. The line 73 in this in stance, is provided with a combination variable orifice and reverse valve 128. Line 73 communicates with a middle port 130 in the casing of valve 128 while forward and reverse lines 131 and 132 extend from ports 133 and 134, disposed on either side of port 130;to

corresponding forward and reverse ports of the motor 127. Ports 135 and 136 arranged between inlet port 130 and ports 133 and 134, are connected by line 137 with one end of a spool chamber 138 of a selector and regulator spool 140. The opposite end of this valve chamber 138 is connected with passage 73 by branch line 141. Valve 128 has a spool 142 disposed for longitudinal movement therein to control communication between ports 130, 133, 134, 135, 136 and exhaust ports 143 disposed at opposite ends of of the valve 128 and connected by line 144 with 'lines 65 leading to the inlet ports 63 of pump 56. Spool 142 is shaped at opposite sides of its middle land so that when the spool is centered the middleport 130 is closed and line 73 is blocked. Movement of the spool 142 to the left will cause an increase in the area of the annular orifice formed between the spooland edges of the casing at middle port or groove 130 between middle port 130 and port 136. Movement of the spool 142 to the right from the above mentioned middle position will, of course, open the orifice formed between spool 142 and the edges of the casing at middle port or groove 130 between middle port or groove 1 30 and port 135. The area of either of the orifices is, therefore, a function of the position of spool 142 in the casing of valve 128. The purposes of these orifices will be made apparent later in the description. The valve 128 serves to connect either of the motor ports 133 and 134 with the line 73 and the other motor port with exhaust line 144 through one of the exhaust ports 143 to cause, the operation of the motor 127. In the event the motor 127 should tend to overrun and demand more fluid than is being supplied through line 131 or 132 then serving as the inlet, fluid will be drawn through line 145 leading directly from the reservoir 64 and through one of the check valves 146, to supply additional fluid to said line 131 or 132.

Suitable means, represented by an electric torque motor 147 may be provided to control the movement of: spool 142 in the operation of the system. A spring 148'; maintains the spool 142 in engagement with the movable element 150 of the motor 147 and causes it to move in unison therewith. Motor 147 has a rotatable armature, which is used to actuate the movable element 150 in response to electric current supplied to the terminals 151 The displacement of the element 150 along the axis of the spool 142 is proportional to the strength of the elec-- tric current applied to the terminals 151.

Valve mechanism 140 is similar in construction and.

operation to valve 36 in the form of the invention first described. It includes a casing 152 forming a spool. chamber having inlet ports 153, 154 and 155. corre sponding in number to and connected with the diflierent sets of output ports 66, 67 and 68, respectively, of pump 56 in Fig. 4. The casing 152 also has ports at opposite ends of the chamber to which lines 137 and 141 connect. and an exhaust port 156 connected. with exhaust line. 144. The spool chamber receives a spool 157 for sliding, movement from a position at one end of the chamber, as; illustrated, in which the inlet ports 153, 154 and are disconnected: from the exhaust port 156, to other positions in which. one or more of the inlet ports 153, 154 and155 are connected with the exhaust port 156. Spool 157 is a. composite element so formed as to provide a. socket for a relatively long spring 158, used to urge the.

spool toward the first position, and yet provide a passage for connecting the inlet and exhaust ports. The spool 157 has a plurality of ports 160, 161 and 162 so located that as the spool 157 moves one or more of the inlet" 11 ports 153, 154 and 155 will be connected with exhaust port 156.

Whenoperation of the system shown in Fig. 4 is initiated and valve spool 157 is in the position shown it will cause the entire output of the pump 56 to be directed to line 73 since ports 153, 154 and 155 are blocked by spool 157. This condition will continue only if valve spool 142 is in a position to direct the full pump volume to fluid motor 127. When valve spool 142 is in the middle or centered position shown and pump 56 is in operation, valve spool 157 of valve 140 will occupy a position adjacent the left end of the casing 152 so that all the pump output volume will be returned through valve 140 and lines 144 and 65 to the inlets 63 of the pump. The valve 140 functions substantially the same as valve 36 in the first form of the invention. The pressures on opposite sides of either of the orifices formed by the spool 142 in its casing are applied to opposite ends of the spool 157, the higher pressure being applied to the end opposite that engaged by the spring 158. These pressures will hold the spool in position to by-pass the portion of the pump output in excess of that necessary to maintain the pressure differential. If the portion by-passed is suflicient to permit any of the pumping sections of the pump to operate without load, the pumping section or sections so unloaded will require only the operating horsepower necessary to overcome the friction in the pump and lines. The speed and direction of operation of the motor 127 will be controlled by the position of the valve spool 142. Since the orifice formed by the valve 142 and its casing is arranged in the line leading to the motor, the valve 140, which is controlled by the pressure diiierential caused by the orifice will bypass the fluid not needed to drive the motor. Under certain conditions of operation, portions of the operating horsepower will be conserved as in the other forms of the invention described.

In the form of the invention shown in Fig. 4, fluid pressure may tend to increase when the valve spool 142 is centered because there is then no outlet leading from. line 73. At such time, however, the pressure in line/7.3 will be applied through line 141 to the end of spool 157 and spool 157 will be moved to force the fluid at the left end of chamber 138 into line 137, thus pressure will exist in line 137 and it will be applied to a relief valve 163 connected with this line. When a predetermined pressure "in line 137 is reached valve 163 will permit fluid to flow from the left end of chamber 138 to the reservoir through line 145 and spool 157 will move in opposition,

to spring 158 until suflicient pump volume is by-passed through valve 140 to prevent the increase in pressure in line 73.

In Figs. to 9 inclusive there is shown an automatically operated mechanism for securing a variable delivery of fluid from a pump. With the mechanism shown in Fig. 5, an infinite variation of fluid delivery from maximum volume to zero may be secured while the operating power requirement will be reduced in increments from a predetermined maximum to a pro-selected minimum.

In this form of the invention a pump 165 with two sets of pumping sections, 166 and 167, and outlet ports, 168 and 170, 170A, is employed. This pump is substantially identical with the pump shown in Fig. 1, except the outlet ports 170, 170A of one set are not directly connected. The reason for their separation will be made apparent hereinafter. This pump has a set of inlet ports 171 connected with a reservoir 172 by lines 173. A

rotor 174 with vanes 175 is arranged to revolve in a cam ring 17 6 forming a peripheral wall 177 for the rotor chamber. The wall 177 is so formed that one part of the total output of the pump will be delivered through ports 168, line 178 leading from ports 168 and the remainder of the output of the pump is through ports 170 and 170A and lines 180 and 181 leading from ports 170, 170A, respec-' tively.

and 194. Grooves 190 and 193 are connected by passage.

195 with reservoir 172. Grooves 189 and 191 are connected by passage 196. A passage 197 connects groovev 188 with line 183, a variable orifice 198 being arranged in passage 197 for purposes to be later pointed out. Lines 178 and 181 connect with passage 197, spring pressed check valves 200 being arranged in these lines to prevent reverse flow from line 197 thereto. Line isconnected'.

with one end of spool chamber 186 and line 181 is connected with the opposite end. Line 180 is also con-f nected with groove 194 of spool chamber 187. Line 178 is connected with groove 192 of chamber 187. Spool is urged toward one end of its chamber, the right end as viewed in Fig. 5, by a spring 201. Fluid passages 202; and 203 lead from the inlet and outlet ends of the orifice.

198 to opposite ends of the spool chamber 187, the outlet pressure being applied to the end engaged by the spring.

The operation of the form of the invention shown in Figs. 5 to 9, inclusive, is as follows: Rotation of the rotor.

174 in the direction indicated by the arrow in Fig. 5 will.

cause fluid to be drawn into the rotor chamber through,

ports 171 and to be expelled through outlets 168, 170'and 170A, one third of the pumps total output issuing from ports 168, one third from port 170 and the rest from port 170A. All this fluid will be combined in line 197 and flow through orifice 198, when it is fully open, to line 183, fluid from port 170 flowing through line 180 to chamber 186, groove 188 and line 197.

When orifice 198 is adjusted progressively to decrease the size thereof, fluid pressure will increase equally in outlet ports 168, 17 0 and 170A and all chambers, grooves and passages communicating therewith and on the high pressure side of orifice198. As fluid flows through the orifice 198 a pressure diiferential is created, the contrasting pressures of which are applied to opposite ends of spool 185. Since the higher pressure is applied to the end of the spool opposite that engaged by the spring 201 the spool will move against the force of the spring as the pressure increases, this movement being toward the left as viewed in Figs. 5, 6, 7, 8 and 9. Movement of thespool in this direction causes a groove 204 therein to establish communication between grooves 191 and 192 as shown in Fig. 6, and some of the fluid from ports 168 may then flow from line 178 to reservoir 172 through grooves 192, 204 and 191, line 196, groove 189, groove 205 in spool 184, groove and line 195, this line also being connected with groove 193. Further adjustment tween grooves 193 and 194 at which time part of the output from port 170 will be by-passed to reservoir 172. This fluid will flow through line 180 to grooves 194, 206 and 193 and through line 195 to the reservoir 172. Until spool 185 has moved far enough to the left to by-pass fluid from port 170, the pressure in port 170 and line 180 will be applied to the left end of spool 184 to retain it in position at the right end of its chamber as shown in Fig. 7. During this time the output from port 170 will fiow through groove 188 to line 197.

When orifice 198 is reduced enough to cause spool 185 to move far enough to the left to by-pass all of the fluid issuing from port 170, the pressure in line 180 and the left end of chamber 186 connected therewith will drop to that existing in reservoir 172. Since the pressure in the right end of chamber 186 is still the same as that in line 181, spool 184 will quickly move to the left and interrupt communication between groove 188 and line 197 and between grooves 189 and 190. The spool elements 184 and 185 will then occupy the positions shown in Fig. 8, in which the output from port 168 through line 178 will be prevented from being by-passed to the reservoir and will be directed to line 197. In these positions of spools 184 and 185 both ports 170 and 170A will be completely by-passed to reservoir 172; fluid from port 170 will flow through line 180 to groove 194, through groove 206 to groove 193 and thence through line 195 to the reservoir. Fluid from port 170A will flow through 1ine181 the right end of spool chamber 186, groove 190 andline 195 to the reservoir. Since all the outputfrom ports 170 and 170A is being by-passed under substantially no pressure, the operating power requirement of the pump will be reduced proportionately as before. At this time (see Fig. 9) spool 185 functions as a flow control to regulate the volume of fluid from ports 168 by by-passing part to the reservoir from line 178 through grooves 192,. 207 in spool 185, 193 and line 195. It will be seen that the volume of fluid flowing to the work may be controlled merely by the adjustment of one element, the variable orifice 198.'

As in the other forms of the invention illustratedthe valve mechanism will function to maintain a flow of predetermined volume if the rate of operation of the pump is varied.

If the orifice 198 has previously been adjusted to give a low volume and it is desired to select a higher volume, the orifice is adjusted to increase its size. This operation decreases the pressure at the inlet side of the orifice and permits spring 201 to move the spool 185 toward the right. As the spool moves from the position in which the discharge from both ports 170 and 170A and part ofthe discharge from ports 186 is being by-passed it moves to a position in which only ports 170 and 170A are connected with exhaust. Continued increase in the size of theorifice will cause continued movement of spool 185 toward the right until groove 206 no longer connects grooves 193 and 194. When this communication is interrupted the pressure in line 180 will cause spool 184 to shift to the right to reestablish a connection between grooves 189 and 190. At this time all of the output from pump ports 170 and 170A will be directed through line 197 and all or part of the output from ports 168 will be directed to exhaust.

It will be observed from the foregoing description and the drawings that while the principles of operation of all forms of the volume regulating valve mechanism shown are the same, two types of results are secured merely by different arrangements of the passage forming means in the valve spools. Figs. 1, 3 and 4 have the spool ports so arranged that the sets of output ports of the pump are successively connected with exhaust to secure a cumulative effect in the by-passing of fluid. As each set of output ports is completely vented to exhaust under no pressure, the operating power requirement of the pump will be reduced in the same proportion that the volume issuing from the vented ports bears to the total pump volume. In the form of the invention shown in Fig. 1, the pump has two sets of output ports and one reduction in operating power requirement may be secured. In the form of the invention shown in Fig. 5, the same pump is employed but :two different reductions in operating power requirements may be secured because of the arrangement of the passage-forming means in the valve mechanism. This valve mechanism functions to connect either of the two sets of pump output ports with exhaust, therefore, by constructing the pump with pumping sections of difierent volumes different reductions in horsepower requirements may be secured. In Fig. 2 as previously explained a pump with three pumping sections is provided. The volume control valve is so constructed that each pumping section maybe individually connected with exhaust as may also any combination of pumping sections thus providing six reductions in operating power requirements. Because each reduction may be a smaller fraction of the total horsepower they may be caused to occur earlier in the operation of the mechanism than when larger reductions are secured.

The form of the invention shown in Fig. 5, utilizes a pump with two sets of pumping sections. It will be obvious that a similar mechanism suitably modified may be employed if a pump with additional sets of pumping sections is to be used.

From the foregoing it will be apparent that a source of fluid pressure has been provided which will function the same as a variable volume pump. The operation of a single control will result in the selection of a desired volume and in certain instances, the limitation of power required to elfect the operation of the pumping means. The single control can be either manually, mechanically or electrically operated depending upon the desires of the manufacturer. The mechanism is adaptable to many different uses. 1

While the form of embodiment of the present invention as herein disclosed constitutes a preferred form, it is to be understood that other forms might be adopted, all coming within the scope of the claims which follow.

We claim:

1. A hydraulic pressure source comprising a pump having a plurality of pumping sections with separate outlets; a passage communicating with said outlets; orifice means in said passage for resisting fluid flow therethrough to create a pressure differential; valve mechanism having a casing forming a chamber With an outlet port and a plurality of inlet ports, each inlet port communicating with ardiflerent outlet of said pump; a spool valve disposed for movement in said casing, said spool being provided with passage forming means arranged to connect one of said inlet ports with the valve outlet port in one position of said spool and a plurality of said inlet ports with said valve outlet port in difierent positions of said spool; resilient. means tending to move said spool to a position in which the valve inlet ports are unconnected with the valve outlet port; and a passage means for applying the contrasting pressures of the pressure differential created by said orifice to opposite ends of said spool to move the same in opposition to said resilient means.

2. A hydraulic pressure source comprising a pump having a plurality of pumping sections with separate outlets;

a passage communicating with said outlets; a check valve between said passage and each of said outlets to prevent. fluid flow from said passage to said outlets; orifice means in said passage for resisting fluid flow therethrough to create a pressure differential; valve mechanism having means forming. a chamber with an outlet port and a plurality of inlet ports, each inlet port communicating with a different outlet of said pump; a spool valve disposed for movement in said casing, said spool being provided with passage forming means arranged to connect one of said inlet ports with the valve outlet in one position, an-

other of said inlet ports with said valve outlet in a second position and both of said inlet ports with said valve outlet in a third position, resilient means urging said spool toward a position in which no inlet port is connected with said valve outlet; and passage means for applying the pressure difierential created by said orifice to opposite ends of said spool to move the same in opposition to said resilient means.

3. A hydraulic pressure source comprising a pump having a plurality of pumping sections with separate outlets; a passage connected with said outlets; a variable orifice in said passage to resist fluid flow therethrough to create a pressure differential; valve mechanism having means forming a chamber with an outlet port and a plurality of inlet ports, each of said inlet ports communicating with a difierent outlet of said pump; a spool valve disposed for movement in said chamber, said spool being provided with passage forming means arranged to connect one of said inlet ports with said valve outlet in one position of said spool and different combinations of said inlet ports with said valve outlet in different positions of said spool; spring means tending to move said spool toward a position in which no inlet port is connected with said valve outlet; and passage means for applying the pressure differential created by said orifice to opposite ends of said spool to move the same in opposition to said resilient means.

4. In a hydraulic pressure source comprising a pump having a plurality of pumping sections with separate outlets; a passage communicating with said outlets; check valve means between said passage and each outlet; a variable orifice in said passage to resist fluid flow therethrough and create a pressure differential; valve mechanism having means forming a chamber with an outlet port and aplurality of inlet ports, each inlet port communicating with a different outlet of said pump; a spool valve disposed for movement in said chamber, said spool being provided with passage forming means arranged to connect the various inlet ports with said valve outlet port in difierent positions of said spool and different combinations of said inlet ports with said valve outlet port in other positions of said spool, said means being formed to maintain the connections between the inlet ports connected with the larger capacity pump outlets and said valve outlet during a greater length of movement of said spool than the length of movement during which the connection between the inlet ports connected with the smaller capacity pump outlets and said valve outlet is maintained; and passage means for applying the pressure diflerential created by said orifice to the opposite ends of said spool to cause movement from a position in which no inlet is connected with said pump outlet to said other positions.

5. A hydraulic pressure source comprising a pump having a plurality of pumping sections with separate outlets; a passage communicating with said outlets; orifice means in said passage for resisting fluid flow therethrough to create a pressure difierential; valve mechanism having a casing forming a chamber with an outlet port and a plurality of inlet ports, each inlet port communicating with adifferent outlet of said pump; a spool valve disposed for movement in said casing, said spool being provided with passage forming means arranged to connect one or more of said inlet ports with the valve outlet port in different positions of said spool; resilient means tending to move said spool to a position in which the valve inlet ports are unconnected with the valve outlet port; passage means for applying the pressure differential to opposite ends of said spool to move the same in opposition to said resilient means; means for resisting the flow of fluid from the outlet of the valve chamber to create pressure; and a jet type booster responsive to such pressure to supercharge said pump.

6. A hydraulic pressure source comprising a pump having a plurality of pumping sections with separate outlets; a passage communicating with said outlets; orifice means in said passage for resisting fluid flow therethrough to create a pressure differential; valve mechanism having a casing forming a chamber with an outlet port and a plurality of inlet ports, each inlet port communicating with a different outlet of said pump; a spool valve disposed for movement in said casing, said spool being provided with passage forming means arranged to connect one or more of said inlet ports with the valve outlet port in different positions of said spool; resilient mean tend- 16 ing to move said spool to a position in which the valve inlet ports are unconnected with the valve outlet port; passage means for applying the pressure differential to opposite ends of said spool to move the same in opposi tion to said resilient means; a reservoir, a passage leading from the valve chamber outlet to said reservoir;'fiow resisting means in the last-mentioned passage to create a pressure; a fluid passage extending from said reservoir to said pump; and a jet type booster in the last-mentioned passage, said booster being responsive to the pressure in the line leading from said valve chamber outlet to draw. fluid from said reservoir and direct it to said pump.

7. A hydraulic pressure source comprising a pump hav ing a plurality of pumping sections with separate Outlets;

a passage communicating with said outlets and leading.

to a point of use; check valves between-said passage and said pump outlets to prevent flow from the former, to the latter; valve mechanism having means forming a chamber with an outlet and a plurality of inlet ports, each inlet port being connected with a different pump outlet; a spool valve disposed for movement in said chamber, said spool valve having passage forming means arranged to connect one of said inlet ports with said valve outlet in one position of said valve spool and combinations of said inlet ports with said valve outlet in difierent positions of said, spool; spring means tending to move said spool to a position in which all inlet ports are 1111- connected with said outlet port; a combination variable orifice and reversing valve creating a pressure differential; and passage means for applying the contrasting pressures. of said differential to opposite ends of said spool,,the diflerential pressure serving to move said spool inopposition to said spring.

8. A hydraulic pressure source comprising a pump having a plurality of pumping sections with separate outlets; a passage communicating with said outlets; valve mechanism having a casing forming a chamber with an exhaust port and a plurality of inlet ports, each inlet port communicating with a different outlet of said pump; a valve element disposed for movement in said chamber to connect one or more of said inlet ports with said exhaust port; variable orifice means in said passage to. create a pressure differential said orifice means having relatively movable elements; passage means extending from'the inlet and outlet sides of said orifice to'opposite ends of said valve chamber to apply the differential pressure to said valve element to move the same; and electromotive means engaging one element of said orifice to move the same to vary the effective size of such orifice.

9. A hydraulic pressure source comprising a pump hav ing a plurality of pumping sections with separate outlets; a passage communicating with said outlet; valve mechanism having a casing forming a chamber with an exhaust port and a plurality of inlet ports, each inlet port communicating with a difierent outlet of said pump; a valve element disposed for movement in said chamber to connect one or more of said inlet ports with said exhaustport; variable orifice means on said passage to create a,

pressure diiferential said orifice means having relatively movable elements; passage means extending from the in-.

let and outlet sides of said orifice to opposite ends of said valve chamber to apply the differential pressure to said valve element to move the same; and an electro': torque motor engaging one element of said orifice to move the same in response to current variations to change sure difierential; an element responsive to such pressure differential to by-pass to exhaust varying quantities of fluid from one or more of said pumping sections depending upon the amount of fluid issuing from said pumping sections in excess of that required to maintain said pres sure differential, said element including opposed portions, and means for applying the pressures of said pressure diiferential to said opposed portions for rendering said element responsive to said pressure differential as aforesaid.

11. A fluid pressure source comprising a pump having a plurality of separate pumping sections with separate outlets; a main pressure delivery conduit; a separate pressure delivery conduit leading from each outlet to said main pressure delivery conduit; a check valve between said main pressure delivery conduit and each of said separate pressure delivery conduits to prevent fiow from the former to the latter; an orifice in said main pressure delivery conduit; a valve mechanism having means forming a casing with an exhaust port and a plurality of separate inlet ports, each of said inlet ports being con nected with a different pump outlet; a valve element disposed in said casing for stepless movement between a position obstructing communication between all of said inlet ports and said exhaust port and a position in which all of said inlet ports are substantially fully connected with said exhaust port; means resiliently urging said valve element toward the former position; and passage means connecting said main pressure delivery conduit at the inlet and outlet sides of said orifice with said valve casing at opposite ends of said valve element, the pressure from the inlet side of said orifice opposing said resilient urging means.

12. Hydraulic apparatus comprising a pump having a plurality of pumping sections with an inlet and separate outlets; means forming a fluid delivery port and a passage leading thereto; means forming an orifice in said passage for resisting fluid flow therethrough to create a pressure difierential; valve mechanism having means forming a chamber and a plurality of spaced ports, one of said ports communicating with said pump inlet and each of the remaining ports communicating with a different pump outlet, all of the latter ports being connected with said passage; and valve means disposed for move ment between different positions in said chamber, said valve means forming passages arranged to successively connect the ports communicating with the pump outlets with the port communicating with the pump inlet, said valve means being responsive to and moved by the pressure differential caused by said orifice.

13. Hydraulic apparatus comprising a pump having a plurality of pumping sections with an inlet and separate outlets; means forming a fluid delivery port and a passage leading thereto; means forming an orifice in said passage for resisting fiuid flow therethrough to create a pressure differential; valve mechanism having means forming a chamber and a plurality of spaced ports, one of said ports communicating with said pump inlet and each of the remaining ports communicating with a different pump outlet, all of the latter ports being connected with said passage; check valve means between said latter ports and said passage to prevent flow from the passage to said ports; and valve means disposed for movement between different positions in said chamber, said valve means forming passages arranged to successively connect the ports communicating with the pump outlets with the port communicating with the pump inlet, said valve means being responsives to and moved by the pressure differential caused by said orifice.

References Cited in the file of this patent UNITED STATES PATENTS 2,074,618 Roeder Mar. 23, 1937 2,247,261 Towler et al. June 24, 1941 2,276,895 Vosseler et a1 Mar. 17, 1942 2,419,375 Shartle Apr. 22, 1947 2,432,502 Bentley Dec. 16, 1947 2,475,413 Towler et a1. July 5, 1949 2,549,897 Evrell Apr. 24, 1951 2,568,356 Moulden Sept. 18, 1951 2,611,245 Strehlow Sept. 23, 1952 2,611,319 Strehlow et a1 Sept. 23, 1952 2,618,932 Taup Nov. 25, 1952 2,696,788 Funston Dec. 14, 1954 2,746,392 Klessig et a1. May 22, 1956 2,768,582 Klessig et a1. Oct. 30, 1956 FOREIGN PATENTS 559,108 Great Britain Feb. 4, 1944 

